Antioxidant Benzophenones and Biphenyls from an Endophytic Fungus Penicillium sp. QM-4.

The endophytic fungi from plants are recognized as a valuable source of structurally diverse secondary metabolites with intriguing bioactivities. Three previously undescribed compounds, including two benzophenones, 2-(2,6-dihydroxy-4-methylbenzoyl)benzoic acid (1) and 2-(2,6-dihydroxy-4-(hydroxymethyl)benzoyl)benzoic acid (2), one biphenyl, 4',5,5'-trihydroxy-3-methoxy-2'-methyl-(1,1'-biphenyl)-2-carbaldehyde (4), along with two known compounds (3 and 5), were isolated from the endophytic fungus Penicillium sp. QM-4 associated with Pteris cretica. Their structures were established by extensive spectroscopic analysis of HRESIMS, UV, IR, and 1D and 2D NMR data. Free radical scavenging activity of compounds 1-5 was assessed, and compound 3 displayed a significant antioxidant effect in the DPPH assay. Structure-activity relationships of compounds 1-3 were also discussed. These findings enrich the structural diversity and bioactivities of benzophenones and biphenyls derived from fungal source.